Piston and connecting rod assemblies of hydraulic pump or motor

ABSTRACT

Piston and connecting rod assembly for hydraulic pump or motor, wherein a piston comprising a chamber of substantially cylindrical configuration with a bottom of at least partspherical shape corresponding to a part-spherical surface of the oscillating connecting rod adapted to be engaged therein, characterized in that said chamber has its longitudinal axis inclined in relation to the piston axis by an angle greater than the angle of oscillation of the connecting rod during the actual operation of the assembly, said chamber comprising a partspherical retaining surface matching a corresponding surface of the connecting rod and having its center coincident with that of said bottom spherical surface of the piston, but with a greater radius than said last-named surface, whereby when said connecting rod has been engaged home onto said chamber it is retained therein between said bottom surface and said retaining surface when its axis corresponds to the operative position of the two parts.

United States Patent [72] Inventor Francois C. Pruvot Billancourt, France 2| Appl. No 27,871 [22] Filed Apr. 13, I970 {45] Patented June 29, 1971 [731 Assignees Regie Nationule Des Usines Renault Billancourt, France; Automobiles Peugeot- Paris, France 32 Priority Apr.2l,l969 France [31] 69/12445 [54] PISTON AND CONNECTING ROD ASSEMBLIES 0F HYDRAULIC PUMP 0R MOTOR 2 Claims, 1 Drawing Fig.

[52] U.S. Cl 287/21, 92/187 [5 I] Int. Cl Fl6c 11/06 [50] Field of Search. 287/20 P, 21', 92/187 [56] References Cited UNITED STATES PATENTS 1,499,964 7/1924 Bell 287/20 P 3,095,221 6/1963 Kaup Primary Examiner-David J. Williamowsky Assistant Examiner-Andrew J. Kundrat Attorney-Stevens, Davis, Miller & Mosher ABSTRACT: Piston and connecting rod assembly for hydraulic pump or motor, wherein a piston comprising a chamber of substantially cylindrical configuration with a bottom of at least part-spherical shape corresponding to a part-spherical surface of the oscillating connecting rod adapted to be engaged therein, characterized in that said chamber has its longitudinal axis inclined in relation to the piston axis by an angle greater than the anglept' oscillation of the connecting rod during the actual operation of the assembly, said chamber comprising a part-spherical retaining surface matching a corresponding surface of the connecting rod and having its center coincident with that of said bottom spherical surface of the piston, but with a greater radius than said last-named surface, whereby when said connecting rod has been engaged home onto said chamber it is retained therein between said bottom surface and said retaining surface when its axis corresponds to the operative position of the two parts.

PlSTON AND CONNECTING ROD ASSEMBLIES OF HYDRAULIC PUMP OR MOTOR The present invention relates to improvements in piston units for hydraulic pumps or motors of the type intended for the pumping of compressible or incompressible fluids, more particularly those wherein the cylinder forming bores are disposed at spaced angular intervals about a common axis within a barrel body and adapted to revolve about said axis, the pistons being associated with connecting rods and performing oscillatory movements in relation to the piston during the operation.

In a known construction a reciprocating piston is assembled to a ball joint rigid with the rod, the latter being retained by,

means corresponding in shape to the surface of said ball.

A known inconvenience of this construction lies in the complicated machining of the piston.

Another structure comprises a piston crimped to the ball member, which consists of a hollow cylinder closed at one end and provided with a lubricated bearing member for the ball joint or member, adapted to absorb stresses developing between the piston and rod without seizing.

The inconveniences characterizing this last-mentioned arrangement are due to the crimping of the piston to the ball member, the inadequate piston guiding and the relatively rapid piston wear.

Piston and connecting rod assemblies are already known wherein the bearing ball joint is secured by crimping to the piston. This arrangement, in which the bearing has only good frictional properties, is ill suited for high-pressure pumps for the rod ball joints must have a relatively small diameter in all cases.

Other assemblies are known wherein the piston made of low hardness steel is crimped directly to the ball shaped member.

This arrangement requires an accurate grinding of the piston after the crimping operation and precludes any checking of the ball joint play and any subsequent disassembling of the unit.

It is the essential object of the present invention to avoid the inconveniences set forth hereinabove by providing a piston and connecting rod assembly comprising in the piston a substantially cylindrical chamber having its bottom at least par tially shaped to match a spherical end surface of the oscillating connecting rod associated therewith, this assembly being characterized in that said chamber has its longitudinal axis inclined in relation to the piston axis by an angle greater than the angle of oscillation of the connecting rod during the actual operation of the assembly, said chamber being formed with a part-spherical retaining surface matching a corresponding surface of the connecting rod and having its center coincident with that of said bottom spherical surface of the piston, but with a greater radius than said last-named surface, whereby when said connecting rod has been engaged home into said chamber it is retained between said bottom surface and said retaining surface when its axis corresponds to the operative position of the two parts.

A typical form of embodiment of a piston and connecting rod assembly according to invention will now be described by way of example with reference to the single FIG. of the attached drawing, which shows a diagrammatic longitudinal section of this assembly.

The assembly illustrated comprises connecting rod 1 having its piston-engaging end designed as a ball joint 2. This ball joint comprises two part-spherical surfaces '3 and 4 having a common center but different radii, the radius R2 of spherical surface 4 being greater than the radius R1 of spherical surface 3. These part-spherical surfaces are limited by cylindrical surfaces 6 and 7 of same diameter 111, and between these two cylindrical surfaces 6 and 7 the connecting rod comprises a tapered connecting surface having its small end near the cylindrical surface 6 to permit the fitting of the connecting rod into the piston and its oscillation therein, as will be explained presently.

The piston 8 of generally cylindrical configuration has an outer diameter and a length calculated to permit the sliding movement of the piston in a cylinder" forming bore (not shown).

in fact, this piston 8 has formed therein a blind cylindrical hole 9 having a diameter d2 ending with a semispherical bottom surface 10 having the same radius R1 as the part-spherical surface 3 of the connecting rod. The cylindrical hole 9 has an axis of revolution (x) forming a certain angle 13 with the piston axis (y). These two axes converge to a point 0 constituting the center of the part-spherical surface 10 having the aforesaid radius R1. This angle 13 is greater than the maximum angle 14 formed between the rod axis and the piston axis during the actual operation of the hydraulic pump or motor, say, twice this maximum angle 14.

The piston 8 is formed with a circular groove 11 coaxial with the piston and the rear face 12 of this groove has a partsphcrical configuration having the same radius R2 as the partspherical surface 4 of connecting rod 1, the center of this face 12 being coincident with the center 0 of the surface of radius R1 machined in the piston bottom.

With a connecting rod diameter d1 slightly inferior to the diameter d2 of the hole formed in the piston, the connecting rod can penetrate into the hole 9 in an angular position 13 until its semispherical surface 3 engages the semispherical surface 10 of the piston. Then the connecting rod can be straightened so that its axis be aligned with the piston axis. The part-spherical surface 4 of the connecting rod 1 will then substantially engage the spherical retaining surface 12 of same radius, machined in the piston bore.

From this position the connecting rod can oscillate in all directions with an amplitude equal to the angle 14 which is substantially equal to half the magnitude of angle 13 while remaining axially connected to the piston.

The piston has an axial hole 15 formed therethrough to permit the proper lubrication of the part-spherical surfaces.

From the above description it will be clearly apparent that the method of manufacturing and assembling the two component elements of this assembly are particularly simple.

The assembly according to this invention is applicable notably to all hydraulic barrel-type connecting rod pumps and motors, and more particularly to so-called hinged shaft" pumps and motors. However, the same arrangement is also applicable to other types of motors, such as hot-gas motors for power-assisted controls as used notably in rockets, missiles and the like, wherein the piston could be sintered and impregnated with lubricant so that a short-time operation under difficult temperature conditions can be achieved.

This assembly comprising only two elements and its extremely simple assembling method (without resorting to any crimping of screwing operation) is particularly suited for mass production purposes. I

It will be apparent that obvious variations may be brought to the above-described form of embodiment without however departing from the basic principles of the invention as set forth in the appended claims.

lclaim:

l. Piston and connecting rod assembly for hydraulic pump or motor, wherein a piston comprising a chamber of substantially cylindrical configuration with a bottom of at least partspherical shape corresponding to a part-spherical surface of the oscillating connecting rod adapted to be engaged therein, characterized in that said chamber has its longitudinal axis inclined in relation to the piston axis by an angle greater than the angle of oscillation of the connecting rod during the actual operation of the assembly, said chamber comprising a partspherical retaining surface matching a corresponding surface of the connecting rod and having its center coincident with that of said bottom spherical surface of the piston, but with a greater radius than said last-named surface, whereby when said connecting rod has been engaged home into said chamber it is retained therein between said bottom surface and said retaining surface when its axis corresponds to the operative position of the two parts.

2. Assembly according to claim 1, characterized in that a spherical surface of the connecting rod mates with said partspherical retaining surface, said connecting rod comprises two cylindrical surfaces adjacent said part-spherical surfaces but 

1. Piston and connecting rod assembly for hydraulic pump or motor, wherein a piston comprising a chamber of substantially cylindrical configuration with a bottom of at least partspherical shape corresponding to a part-spherical surface of the oscillating connecting rod adapted to be engaged therein, characterized in that said chamber has its longitudinal axis inclined in relation to the piston axis by an angle greater than the angle of oscillation of the connecting rod during the actual operation of the assembly, said chamber comprising a partspherical retaining surface matching a corresponding surface of the connecting rod and having its center coincident with that of said bottom spherical surface of the piston, but with a greater radius than said last-named surface, whereby when said connecting rod has been engaged home into said chamber it is retained therein between said bottom surface and said retaining surface when its axis corresponds to the operative position of the two parts.
 2. Assembly according to claim 1, characterized in that a spherical surface of the connecting rod mates with said part-spherical retaining surface, said connecting rod comprises two cylindrical surfaces adjacent said part-spherical surfaces but of a diameter slightly less than that of said chamber, said cylindrical surfaces being interconnected by a tapered surface having its small end adjacent to the cylindrical surface adjacent said part-spherical retaining surface. 